Modeling multidimensional spectral lineshapes from first principles: Application to water-solvated adenine

In this discussion we present a methodology to describe spectral lineshape from first principles, providing insight into the solvent-solute molecular interactions in terms of static and dynamic disorder and how these shape the signals recorded experimentally in linear and nonlinear optical spectroscopies, including two-dimensional electronic spectroscopy (2DES). Two different strategies for simulating the lineshape are compared, in which both the coupling to the intra-molecular vibrations and the influence exerted by the different water distributions attained along a molecular dynamics (MD) simulation are accurately described. The first method accounts for such water arrangements as first order perturbations on the adenine energies computed for a single reference (gas phase) quantum calculation. The second method requires to compute the manifold of excited states explicitly at each simulation snapshot, employing a hybrid quantum mechanics/molecular mechanics (QM/MM) scheme. Both approaches are applied to a large number of states of the adenine singlet excited manifold (chosen because of its biological role), and compared with available experimental data. They give comparable results but the first approach is two orders of magnitude faster. We show how the various contributions (static/dynamic disorder, intra-/inter-molecular interactions) sum up to build the total broadening observed in experiments